There's another strong argument in favor of this point. This [1] is from Unreal's license:
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"7. The Agreement Between You and Epic
a. Amendments
If we make changes to this Agreement, you are not required to accept the amended Agreement, and this Agreement will continue to govern your use of any Licensed Technology you already have access to.
However, if we make changes to this Agreement, you will not be allowed to access certain Epic services or download the Licensed Technology unless you have accepted the amended Agreement. If we make changes, we will provide you with notice, such as by sending an email or giving you notice when you next log into an Epic service."
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So in other words, if they do a bait and switch, you're free to keep using the old license for older versions of the engine. The reason I think this is telling is because they did this in the day and age where basically every EULA comes down to "We can do anything at any time, for any reason, and you can do nothing." For them to actually have this in their terms is a tremendous display of good faith.
Unity may update these Unity Software Additional Terms at any time for any reason and without notice (the “Updated Terms”) and those Updated Terms will apply to the most recent current-year version of the Unity Software, provided that, if the Updated Terms adversely impact your rights, you may elect to continue to use any current-year versions of the Unity Software (e.g., 2018.x and 2018.y and any Long Term Supported (LTS) versions for that current-year release) according to the terms that applied just prior to the Updated Terms (the “Prior Terms”). The Updated Terms will then not apply to your use of those current-year versions unless and until you update to a subsequent year version of the Unity Software (e.g. from 2019.4 to 2020.1). If material modifications are made to these Terms, Unity will endeavor to notify you of the modification. If a modification is required to comply with applicable law, the modification will apply notwithstanding this section. Except as explicitly set forth in this paragraph, your use of any new version or release of the Unity Software will be subject to the Updated Terms applicable to that release or version. You understand that it is your responsibility to maintain complete records establishing your entitlement to Prior Terms."
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EDIT: Oh wow. How sketchy. That page on Github is only their "additional terms". When you go to their terms page itself you find [2]
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"1.4 Modification
Unity reserves the right, at its sole discretion, to modify, discontinue or terminate the Services. Unity may also modify the Agreement at any time and without prior notice. If we modify the Agreement, we will post the modification on the Site or otherwise provide you with notice of the modification. We will also update the “Last updated” date at the top of these Terms. By continuing to access or use the Services after we have provided you with notice of a modification, you indicate that you agree to be bound by the modified Terms. If the modified Terms are not acceptable to you, your only recourse is to cease using the Services.
Notwithstanding this Section 1.4, any modification of the Unity Software Additional Terms is subject to Section 8 of the Unity Software Additional Terms."
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There is some serious lawyerizing going on there that makes this largely incomprehensible to me at least, probably by design.
I can't see how anything less favorable to the devs would not be instantly rejected in court, especially in the EU ?
Speaking of which, I don't see why the Unity using devs can't just keep using the old version of Unity, and therefore never have to accept the new license ?
(Of course I assume that Unity would have made it extra-annoying, because these changes don't just come out like that, but the point here is to give themselves time to find an alternative to Unity.)
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"7. The Agreement Between You and Epic a. Amendments If we make changes to this Agreement, you are not required to accept the amended Agreement, and this Agreement will continue to govern your use of any Licensed Technology you already have access to.
However, if we make changes to this Agreement, you will not be allowed to access certain Epic services or download the Licensed Technology unless you have accepted the amended Agreement. If we make changes, we will provide you with notice, such as by sending an email or giving you notice when you next log into an Epic service."
---
So in other words, if they do a bait and switch, you're free to keep using the old license for older versions of the engine. The reason I think this is telling is because they did this in the day and age where basically every EULA comes down to "We can do anything at any time, for any reason, and you can do nothing." For them to actually have this in their terms is a tremendous display of good faith.
[1] - https://www.unrealengine.com/en-US/eula/unreal